Light-emitting devices such as light-emitting diodes (LEDs) have widely application, like optical display device, traffic lighting, data storage device, communication device, illumination device, and medical device. How to enhance the brightness of the light-emitting diodes is an important topic in the field.
In a generally-known technology, a layer with the material of a band-gap greater than that of the active layer is formed on the p-cladding layer (the material is p-Al0.5In0.5P), such as p-Al0.7Ga0.3As or p-GaP window layer, to increase the light extraction efficiency in the AlGaInP material series light-emitting diode having a p-electrode on the top. In order to enhance the current spreading efficiency, the thickness of the window layer can be increased, such as a 7 μm p-Al0.7Ga0.3As layer, or a 50 μm p-GaP layer by HVPE.
In the classic mechanics, a particle having the lower potential energy can not jump over the energy barrier to another side unless its kinetics energy exceeds the energy barrier. However, from the view of quantum physics, it is possible. The tunneling effect is that a particle can pass the energy barrier higher than the total energy of its own. The tunneling structure normally has a high doping concentration of impurity to increase the mobility of the electrons and/or holes. To increase the tunneling effect probability of the electrons and holes, the tunneling structure thickness needs to be very thin also.